Coating compositions

ABSTRACT

PCT No. PCT/EP91/01052 Sec. 371 Date Dec. 15, 1992 Sec. 102(e) Date Dec. 15, 1992 PCT Filed Jun. 6, 1991 PCT Pub. No. WO91/19750 PCT Pub. Date Dec. 26, 1991.The invention is a coating composition containing an aqueous polyurethane dispersion wherein the polyurethane is prepared from a mixture of polycaprolactone diols and an isocyanate mixture having an NCO functionality of more than 1.5 wherein the ratio NCO:OH is from 0.9:1 to 2.5:1. The polyurethane also can contains functional components capable of salt formation in the aqueous solution. The coating composition is particularly useful for coating flexible substrates such as leather and flexible polymeric materials.

FIELD OF THE INVENTION

This invention relates to coating compositions containing aqueouspolyurethane dispersions, the polyurethanes on which the polyurethanedispersions are based being synthesized from a polyol mixture whichconsists at least predominantly of polycaprolactone diols, and to theuse of the coating compositions for the production of coatings onflexible substrates, preferably on leather, leather substitutes and/orflexible plastics.

BACKGROUND OF THE INVENTION

Coating compositions based on aqueous polyurethane dispersions have beenknown for some time. In general, the polyurethanes on which thepolyurethane dispersions are based are produced by polyaddition ofpolyols with diisocyanates, the co-condensation of components capable ofsalt formation having an advantageous effect on dispersibility.Polyurethane urea dispersions, which are also used as coatingcompositions, are formed in the presence of chain-extending agents, suchas diamines.

RELATED ART

European patent 148 970 describes stable aqueous dispersions ofpolyurethane ureas which may be used inter alia as coating compositionsand impregnating agents for all types of substrates, as binders inpaints, as adhesives and as auxiliaries in the paper industry. Thepolyurethane ureas on which the dispersions are based contain asinternal emulsifier chemically incorporated anionic groups and a mixtureof volatile and non-volatile cations as counterions. The resistance ofthe films to swelling under the effect of water is increased through thecontents of volatile cations while the stability of the films tohydrolysis is increased through the content of non-volatile cations.

Polyurethane urea dispersions containing a co-condensed internalemulsifier are also known from DE-OS 26 24 442. The aqueous polyurethaneurea dispersions described therein are used in DE-OS 36 25 605 for theproduction of aqueous pigment preparations for water-based and,optionally, alcoholic gravure, flexographic and screen printing inks.The pigment preparations obtained are relatively stable to alcohols andto storage and show improved adhesion properties and drying rates.

DE-OS 37 02 615 describes coating compositions and finishes for leatherbased on aqueous polyurethane dispersions. The polyurethanes on whichthe polyurethane dispersions are based are obtained using a polyolmixture consisting of polyester polyols and, optionally, polyetherpolyols and the compulsorily present oleochemical polyols containing atleast three functional hydroxyl groups. The leathers or leathersubstitutes coated and finished with these polyurethane dispersions areentirely satisfactory in such properties as durability, brittleness, wetand dry rubbing resistance, compactness and gloss. In addition, theyhave high fastness values without the toxicologically unsafe aziridineshaving to be used for crosslinking, so that they are particularlysuitable as top coats.

Although the above-described coating compositions based on aqueouspolyurethane dispersions are improved in their properties, it has beenpreferred until very recently, for example in the leather industry forfinishing leather, to apply polyurethanes to leather and leathersubstitutes from organic solution. In the field of printing inks, too,the consumption of solvent-containing inks is still considerably higherin relation to the consumption of water-based inks in which water is thesole liquid component or the principal liquid component besidesalcohols.

Accordingly, there is still a need to improve coating compositions basedon aqueous polyurethane dispersions in their properties, above all intheir adhesion, hardness, resistance to water and alcohols, dryingbehavior and their wetting of the substrate, so that they may be used tothe same extent as solvent-containing polyurethane systems.

Accordingly, the problem addressed by the present invention was toprovide coating compositions based on aqueous polyurethane dispersionswhich are improved in their resistance to alcohols, their adhesion andthe other properties mentioned above.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to coating compositions for flexiblesubstrates containing aqueous polyurethane dispersions, characterized inthat the polyurethanes on which the polyurethane dispersions are basedare synthesized from a polyol mixture consisting at least predominantlyof polycaprolactone diols, an isocyanate mixture having an NCOfunctionality of more than 1.5 in an NCO:OH ratio of 0.9:1 to 2.5:1, afunctional component capable of salt formation in aqueous solution and,if desired, a chain-extending agent.

DETAILED DESCRIPTION OF THE INVENTION

The polyurethane forming the basis of the polyurethane dispersions usedin accordance with the invention are based on a polyol mixtureconsisting completely or partly of polycaprolactone diols. In theirbroad disclosures, DE-OS 26 24 442 and EP-PS 148 970 also namepolycaprolactones among the group of polyester polyols. However, thereis no reference to the fact that specifically polycaprolactone diolsform a suitable basis for polyurethane dispersions for coatingcompositions. In addition, polycaprolactones are understood in DE-OS 2624 442 to encompass the various products obtained when a cyclic lactone,for example ε-caprolactone, is reacted with a polyol, an acid-containingpolyol or a hydroxy acid. However, reactions with hydroxy acids lead toring-opened products which have only one free hydroxyl group. Theseproducts are unsuitable for the purpose according to the invention. Inaddition, polycaprolactones of only one type and not mixtures ofpolycaprolactones are always mentioned as the polyol component.

The polycaprolactone diols used in accordance with the invention areunderstood to be polyester polyols which may be prepared by ring-openingpolymerization of ε-caprolactone and which contain a hydroxyl group ateither end. Products such as these may be industrially produced, forexample, by the so-called Interox process in the presence of Lewis acidsor organic acids or alkyl tin compounds or alkyl titanium compounds ascatalysts at temperatures of 20° C. to around 150° C. Thepolycaprolactone diols produced by this process are preferred for thepurposes of the invention by virtue of their very narrow molecularweight distribution.

The polycaprolactone diols according to the invention are produced byring-opening polymerization of ε-caprolactone with aliphatic and/oraromatic diols. Among the aliphatic diols, saturated, unsaturated,linear and branched diols, such as ethylene glycol, 1,3-butanediol,1,4-butanediol, butenediol, neopentyl glycol, are equally suitable. Themolecular weight and hydroxyl value of the polycaprolactone diols play aparticularly important role in the solution to the problem addressed bythe invention. In the ring-opening polymerization, the degree ofoligomerization and, hence, the molecular weight and hydroxyl value ofthe polycaprolactone diols can be controlled in known manner through thequantitative ratios of the diols to the ε-caprolactones. Suitablepolycaprolactone diols have a molecular weight of 230 to 10,000 andpreferably 1,000 to 5,000 and a hydroxyl value of 15 to 540 andpreferably 25 to 140. Mixtures of various polycaprolactone diolsdiffering in their molecular weight within the stated limits areparticularly preferred. Of these, mixtures of two differentpolycaprolactone diols, in which one diol A has a molecular weight of500 to 2,500 and preferably 1,500 to 2,250 and a hydroxyl value of 40 to225 and preferably 45 to 75 while the other diol B has a molecularweight of 2,500 to 6,000 and preferably 2,750 to 4,000 and a hydroxylvalue of 15 to 55 and preferably 25 to 45, have proved to beparticularly effective. Mixtures of diol A with diol B in a ratio byweight of A to B of 1:10 to 10:1, preferably 2:7 to 7:2 and, morepreferably, 3:1 to 1:3 are particularly suitable. Coating compositionshaving excellent properties, above all in regard to the hardness of thecoatings, are obtained where the above-described polycaprolactone diolmixtures are used.

The polyurethanes forming the basis of the polyurethane dispersions usedin accordance with the invention are based on a polyol mixture, of which60% by weight, preferably 85% by weight and, more particularly, 100% byweight, based on polyol mixture, consists of polycaprolactone diols. Inaddition, the polyol mixture may contain, based on polyol mixture, up to404 by weight and preferably up to 154 by weight of other typicalpolyols, such as polyether polyols, polytetrahydrofuran and/or polyesterpolyols containing on average 2 to at most 4 hydroxyl groups. Quitegenerally, the other polyols used are substantially linear and have amolecular weight in the range from 300 to 20,000 and preferably in therange 500 to 6,000. Examples of polyether polyols are the polymerizationproducts of ethylene oxide, propylene oxide, butylene oxide andcopolymerization or graft polymerization products thereof and thepolyether polyols obtained by condensation of polyhydric alcohols ormixtures thereof and the polyether polyols obtained by alkoxylation ofpolyhydric alcohols, amines, polyamines and aminoalcohols. Taking theabove-mentioned conditions for the polyols into account, polyesters,,polyester amides and polyamides of polybasic, saturated and unsaturatedcarboxylic acids or their anhydrides and polyhydric, saturated andunsaturated alcohols, aminoalcohols, diamines, polyamines and mixturesthereof and also polyterephthalates or polycarbonates may also be usedas a further polyol component. Relatively high molecular weight polymersor condensates, such as for example polyethers, polyacetals,polyoxymethylenes, may also be used as polyol component in the synthesisof the polyurethanes. According to the invention, the polyurethanes onwhich the polyurethane dispersions are based are preferably synthesizedfrom polyol mixtures which consist solely of polycaprolactone diols andwhich, more particularly, consist of the already describedpolycaprolactone diol mixtures containing polycaprolactone diols A and Bhaving the stated molecular weights and hydroxyl values in the statedratios by weight of A to B.

The polyurethanes forming the basis of the polyurethane dispersions usedin accordance with the invention are based on an isocyanate mixturehaving an average NCO functionality of more than 1.5 and preferablyhaving an average NCO functionality of 2 to 3. Suitable isocyanates areany monofunctional isocyanates, diisocyanates and polyfunctionalisocyanates either individually or in admixture providing the averageNCO functionality meets the requirement stated above. Preferredisocyanates are aromatic and aliphatic diisocyanates, such as1,5-naphthylene diisocyanate, 4,4'-diphenyl methane diisocyanate,4,4'-diphenyl dimethyl methane diisocyanate, di- and tetraalkyl diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,3-phenylenediisocyanate, 1,4-phenylene diisocyanate, the isomers of tolylenediisocyanate, optionally in admixture,1-methyl-2,4-diisocyanatocyclohexane, 1,6-diisocyanato-2,2,4-trimethylhexane, 1,6-diisocyanato-2,4,4-trimethyl hexane,1-isocyanatomethyl-3-isocyanato-1,5,5-trimethyl cyclohexane, chlorinatedand brominated diisocyanates, phosphorus-containing diisocyanates,4,4'-diisocyanatophenyl perfluoroethane,tetramethoxybutane-1,4-diisocyanate, butane-1, 4-diisocyanate,hexane-1,6-diisocyanate, dicyclohexyl methane diisocyanate,cyclohexane-1,4-diisocyanate, ethylene diisocyanate, phthalicacid-bis-isocyanatoethyl ester; polyisocyanates containing reactivehalogen atoms, such as 1-chloromethylphenyl-2,4-diisocyanate,1-bromomethylphenyl-2,6-diisocyanate, 3,3 -bis-chloromethylether-4,4'-diphenyl diisocyanate. Sulfur-containing polyisocyanates areobtained, for example, by reaction of 2 mol hexamethylene diisocyanatewith 1 mol thiodiglycol or dihydroxydihexyl sulfide. Other importantdiisocyanates are trimethyl hexamethylene diisocyanate,1,4-diisocyanatobutane, 1,2-diisocyanatododecane, tetramethyl xylenediisocyanate and dimer fatty acid diisocyanate. Aliphatic diisocyanatesare preferred. Of these, cyclic or branched aliphatic diisocyanates,such as isophorone diisocyanate, the already mentioned 1,6-hexanediisocyanate and dicyclohexyl methane diisocyanate, are particularlyuseful.

Another important constituent of the polyurethanes on which thepolyurethane dispersions used in accordance with the invention are basedis a functional group which is capable of salt formation in aqueoussolution and which may be regarded as a kind of internal emulsifier.Dihydroxy compounds of carboxylic acids and/or sulfonic acids are usedas the functional group capable of salt formation in aqueous solution.These compounds may either be used as such or may be prepared in situ.In order to introduce ionizable compounds containing carboxylic acidgroups into the polyurethane, dihydroxycarboxylic acids may be added tothe polyols. Preferred dihydroxycarboxylic acids are2,2-dihydroxycarboxylic acids, among which dimethylol propionic acid isparticularly preferred.

The polymers are present in salt form in the polyurethane dispersionsused in accordance with the invention. The preferred polymers modifiedwith carboxylic acids contain alkali metal salts, ammonia or amines,i.e. primary, secondary or tertiary amines, as counterions. The groupscapable of salt formation may be partly or completely neutralized by thecounterions. An excess of neutralizing may also be used.

If desired, special chain-extending agents containing at least one basicnitrogen atom, such as for example mono-, bis- or polyalkoxylatedaliphatic, cycloaliphatic, aromatic or heterocyclic primary amines,, maybe used. However, it is preferred to use only small quantities andparticularly preferred to use no special chain-extending agent at all.

To produce the polyurethanes particularly suitable for the purposes ofthe invention, polyol mixtures are polymerized with the isocyanatemixture in an NCO:OH ratio of 0.9:1 to 2.5:1 and preferably in an almostequimolar ratio or in a slight excess of isocyanate. To producewater-clear polyurethane dispersions, it is best to use the componentcapable of salt formation, expressed as dimethylol propionic acid, inquantities of I to 30% by weight, preferably in quantities of 2 to 20%by weight and, more preferably, in quantities of 10 to 18% by weight,based on polyol. In addition, transparency depends upon the degree ofneutralization. It is readily possible by conducting a few preliminarytests to determine the quantity of neutralizing agent beyond which asufficient degree of transparency is achieved. In general, as little ofthese substances as possible should be used because otherwise theresistance of the coating film to water might suffer.

Basically, the aqueous polyurethane dispersions may be produced by knownprocesses, for example by the acetone process (D. Dieterich, AngewandteMolekulare Chemie, 98, 133 (1981)) and by the process according to DE 1595 602. New processes for the production of polyurethane dispersions arementioned in DE 36 03 996 in the acknowledgement of the prior art. Thepolyurethane dispersions are preferably produced by the so-calledone-pot process or two-pot process. In the one-pot process, the polyolmixture is predissolved with heating in an inert solvent together withthe components capable of salt formation. The isocyanate mixture is thenadded in the presence of more inert solvent and is polymerized over aperiod of 1 to 6 hours at a temperature of approximately 50° C. toapproximately 120° C. Finally, a strong base capable of ionizing thesalt-forming groups is added. Lastly, water is added under typicalreaction conditions. Vigorous stirring increases the dispersibility ofthe polyurethanes in water. In the two-pot process, the polyol mixtureis reacted with the isocyanate mixture in the usual way. To this end,the polyurethane prepolymer prepared as described above is stirred intoa second water-filled pot and the neutralizing agent and optionally thechain-extending agent are subsequently added.

The polyurethane dispersions used in accordance with the invention havea solids content of more than 25% by weight, preferably in the rangefrom 30 to 60% by weight and, more preferably, in the range from 35 to55% by weight, based on aqueous polyurethane dispersion. They arecharacterized by a viscosity in the range from 0.01 to 150 Pas andpreferably in the range from 0.1 to 10 Pas and by an average particlesize of the polyurethanes in the range from 40 to 400 nm, preferably inthe range from 100 to 300 nm and, more preferably, in the range from 125to 250 nm.

The coating compositions according to the invention contain the aqueouspolyurethane dispersions described above in quantities of 5 to 80% byweight, preferably in quantities of 20 to 75% by weight and, morepreferably, in quantities of 50 to 70% by weight, based on coatingcomposition. The coating compositions contain as further constituentswater, preferably deionized water, in quantities of 2 to 80% by weightand preferably in quantities of 10 to 70% by weight and a water-miscibleorganic solvent in quantities of 0 to 50% by weight and preferably inquantities of 0 to 30% by weight. Suitable water-miscible organicsolvents are, primarily, monohydric aliphatic alcohols containing 1 to 4carbon atoms, such as methanol, ethanol, n- and isopropanol and also n-and isobutanols or mixtures thereof. In addition, the coatingcompositions according to the invention may contain other typicaladditives, such as pigments, wetting agents and preservatives,sedimenting agents and the like in quantities of 0 to 80% by weight,depending on the purpose for which they are to be used. If the coatingcompositions according to the invention are used for coating andfinishing leather and leather substitutes, it is advisable with regardto the aqueous polyurethane dispersions to mix the usual additives, suchas homopolymers or copolymers of acrylic acid and of acrylates withstyrene, acrylamide, acrylonitrile, vinyl acetate and vinyl esters ingeneral and/or vinyl ethers (simplified: polyacrylates), colloidalcasein, modified silicones, with aqueous emulsions of natural orsynthetic waxes or wax esters, foam inhibitors and pigment preparations.

The advantage of the coating compositions and finishes for leathercorresponding to the coating compositions according to the invention isthat particularly high fastness values are obtained without any need touse toxicologically unsafe aziridines or technically complicatedirradiation equipment for crosslinking. Accordingly, they are eminentlysuitable as base coats, but especially as top coats. In addition,leathers coated with them show improved fastness to wet rubbing.

If organic pigments, such as azo pigments, azamethines, azaporphines,quinacridones, flavanthrone, anthanthrone and pyranthrone pigments orinorganic pigments, such as white and colored pigments, or mixed oxidepigments or blended pigments and carbon black are used in the coatingcompositions according to the invention, it is possible to produceexcellent water-based and/or aqueous/alcoholic gravure, flexographic orscreen printing inks for flexible substrates, such as elastic plastics.Printing inks such as these contain the described pigments in quantitiesof 0.5 to 804 by weight, preferably in quantities of I to 70% by weightand, more preferably, in quantities of 2 to 60% by weight, based onprinting ink. In this embodiment also,, it is often useful to useindividual additives from those mentioned above in connection with thecoating of leather, such as polyacrylates and/or wax emulsions.

On the whole, the coating compositions according to the invention aredistinguished by high pigment dispersing power and by good pigmentcompatibility. Application of the coating compositions according to theinvention by known methods gives films having improved film formation(drying), high film hardness, improved film flexibility, adhesion,alcohol resistance, abrasion resistance and flexural elasticity.

The coating compositions according to the invention are produced inknown manner and--where pigments are present--in dependence upon theparticle hardness of the pigments used, for example using stirrers,dissolvers, rotor/stator mills, ball mills, stirred ball mills and inhigh-speed mixers.

The present invention also relates to the use of the coatingcompositions for the production of coatings on flexible substrates,preferably on leather and leather substitutes and/or on flexibleplastics, such as flexible PVC, polyolefins and the like. As mentionedabove, other additives may be present in addition to the aqueouspolyurethane dispersions, the water and optionally the solvents,depending on the purpose for which the coating compositions are to beused. The coatings obtained with the coating compositions according tothe invention have improved adhesion properties, improved pigmentabsorption and higher resistance to alcohols, which are particularlyemphasized among the properties already described.

EXAMPLES General procedure 1

In a polymerization reactor equipped with a stirrer, heating and coolingjacket and a reflux condenser,, the polyols were melted under nitrogen.The component capable of ion formation, dimethylol propionic acid, andthree quarters of the quantity of inert solvent added,, for exampleN-methyl-2-pyrrolidone, were then successively added with stirring. Theisocyanate mixture was then added at temperatures of 50° to 70° C.,after which the reaction mixture was heated to temperatures of 80° to90° C. A free NCO content below 5.5% by weight was established. It isimportant in this regard to bear in mind the fact that, in the chosenmethod of titration (dibutyl amine solution), this value also includesthe consumption of dibutyl amine solution for neutralization of thedimethylol propionic acid. After 4 to 5 hours, the polymerizationmixture was cooled to 60° C. and neutralized, for example with N-methylmorpholine. Finally, water was added after about 30 minutes.

Example 1

Using general procedure 1,, an aqueous polyurethane dispersion wasprepared from:

    ______________________________________                                                           Parts by weight                                            ______________________________________                                        Polycaprolactone diol, molecular                                                                   13.54                                                    weight approx. 2,000, OH value                                                approx. 55 (Capa 222 ®)                                                   Polycaprolactone diol, molecular                                                                    4.51                                                    molecular weight approx. 3,000,                                               OH value approx. 40 (Capa 231 ®)                                          Dimethylol propionic acid                                                                          3.2                                                      N-Methyl-2-pyrrolidone                                                                              8.97                                                    Isophorone diisocyanate                                                                            13.49                                                    N-Methyl morpholine   2.41                                                    Water, deionized     52.91                                                    ______________________________________                                    

General procedure 2

The neutralized prepolymer obtained by general procedure 1 wasintroduced as quickly as possible with stirring into the quantity ofwater mentioned in Example 1. The dispersions were first stirred forabout 1.5 hours at average speed and were then stirred for another 3hours at reduced speed at temperatures of around 60° to 70° C. Thedispersion was then cooled to around 40° C., followed by the addition of10% ammonia (approx. 0.67 part by weight, based on Example 1).

APPLICATION EXAMPLES Example 2 Finishing of furniture leather (crust)Priming

100 Parts by weight of an aqueous pigment preparation were mixed with150 parts by weight of the polyurethane dispersion of Example 1. 60Parts by weight of a wax dispersion, 20 parts by weight of an aqueousflatting aid and 350 parts by weight water were then added. The liquoris sprayed 3 to 4 times. Testing of fastness to rubbing in accordancewith DIN 53 339 shows no damage after rubbing 1,000x on a dry felt andno damage after rubbing 300x on a wet felt. Tests to determine long-termflexural behavior in a Bally flexometer (DIN 53 351) show no damageafter flexing 100,000x (dry) and no damage after flexing 20,000x (wet).

APPLICATION EXAMPLE 2 Production of a printing ink

60 Parts of the polyurethane dispersion of Example 1 having a solidscontent of approx. 35%, based on polyurethane dispersion, were mixedwith 20 parts by weight water, 15 parts by weight isopropanol and 3parts by weight pigment preparations produced in the usual way. Theprinting ink is suitable for screen printing, intaglio printing andflexographic printing and shows rapid drying and excellent adhesion.

APPLICATION EXAMPLES 3 TO 12 Application Examples 3 to 6: inventionApplication Examples 7-12: comparison

The dispersion was prepared by general procedure 2 and printing inkswere subsequently prepared therefrom as described in Application Example2.

    __________________________________________________________________________               Example                                                                       3   4   5  6  7   8  9   10 11  12                                 __________________________________________________________________________    Polyol 1   13.54                                                                             13.0                                                                              18.99                                                                            -- --  -- --  -- --  --                                 Polyol 2   4.51                                                                              4.44                                                                              -- 26.19                                                                            --  -- --  -- --  --                                 Polyol 3   --  --  -- -- 18.73                                                                             -- --  -- --  --                                 Polyol 4   --  --  -- -- --  17.75                                                                            --  -- --  --                                 Polyol 5   --  --  -- -- --  -- 16.2                                                                              -- --  --                                 Polyol 6   --  --  -- -- --  -- --  22.47                                                                            --  --                                 Polyol 7   --  --  -- -- 0.33                                                                              -- --  -- 29.07                                                                             21.76                              Polyol 8   --  --  -- -- --  -- --  -- --  2.87                               Polyol 9   3.2 3.15                                                                               2.89                                                                             2.63                                                                            3.0  2.84                                                                            3.15                                                                               2.91                                                                            2.18                                                                              1.78                               Polyol 10  --  --  -- -- 3.17                                                                              -- --  -- --  --                                 N-methyl-2-                                                                              8.97                                                                              8.83                                                                               8.08                                                                             7.36                                                                            4.51                                                                               7.95                                                                            8.81                                                                               8.10                                                                            3.02                                                                              2.81                               pyrrolidone                                                                   Radical trapper                                                                          0.30                                                                              0.30                                                                              -- -- --  -- --  -- --  --                                 Isophorone 13.49                                                                             --  11.02                                                                            10.04                                                                            14.67                                                                             12.6                                                                             --  -- 9.51                                                                              8.94                               diisocyanate                                                                  Desmodur W --  15.8                                                                              -- -- --  -- 15.75                                                                             14.57                                                                            --  --                                 (dicyclohexylmethane-                                                         4,4'-diisocyanate)                                                            N-Methyl morpholine                                                                      2.41                                                                              2.38                                                                               2.89                                                                             2.63                                                                            2.72                                                                              3.5                                                                              2.37                                                                               2.19                                                                            1.76                                                                              2.13                               Water, deionized                                                                         52.91                                                                             51.77                                                                             56.13                                                                            51.15                                                                            52.87                                                                             55.36                                                                            53.73                                                                             49.76                                                                            54.46                                                                             59.71                              __________________________________________________________________________

    ______________________________________                                        Polyol 1  Polycaprolactone diol                                                         MW: 2000                                                                      OHV: 56                                                             Polyol 2  Polycaprolactone diol                                                         MW: 3000                                                                      OHV: 37                                                             Polyol 3  Polyester polyol synthesized from adipic                                      acid and diethylene glycol                                                    OHV: 60                                                             Polyol 4  Polyester polyol synthesized from adipic                                      acid, diethylene glycol, 1,6-hexane diol and                                  neopentyl glycol                                                    Polyol 5  Polypropylene glycol                                                          OHV: 56                                                             Polyol 6  Polypropylene glycol                                                          OHV: 38                                                             Polyol 7  Polyether polyol based on a natural glycerol                                  MW: 5500                                                                      OHV: 30                                                             Polyol 8  Oleochemical polyol                                                           MW: 1000                                                                      OHV: 160                                                            Polyol 9  Dimethylol propionic acid                                           Polyol 10 Oleochemical polyol                                                           MW: 750                                                                       OHV: 220                                                            ______________________________________                                    

Test for alcohol resistance

The printing inks were knife-coated onto flexible PVC film in a layerthickness of 100 μm and dried for 1 minute at 90° C. After cooling toroom temperature, a cotton wool plug impregnated with ethanol/water(60:40 parts by weight) was applied to part of the surface (the cottonwool plug was covered with a watch glass to prevent it from drying out).

The surfaces were then visually evaluated after 10 to 240 minutes.

    ______________________________________                                        Visual evaluation:                                                                     Appearance of the surface after                                               (minutes)                                                            Example    10    30      60  120    180  240                                  ______________________________________                                        3          5     5       4   4      4    3                                    4          5     5       4   4      4    4                                    5          5     5       4   3      3    2                                    6          5     4       4   3      3    2                                    7          3     2       1                                                    8          3     2       1                                                    10         3     2       1                                                    11         3     2       1                                                    12         3     2       1                                                    ______________________________________                                         5 Points: no change = very good                                               4 Points: slight surface attack = good                                        3 Points: surface affected = adequate                                         2 Points: serious surface attack = poor                                       1 Point: total destruction = inadequate                                  

We claim:
 1. A coating composition for flexible substrates containing anaqueous polyurethane dispersion, wherein the polyurethane dispersioncomprises a polyurethane comprising residues of a block A of apolycaprolactone diol and a block B of a polycaprolactone diol whereinan average molecular weight of the block A is different from an averagemolecular weight of the block B and each of block A and block B fallswithin an average molecular weight of from 230 to 10,000 and a hydroxylvalue of from 15 to 540 and wherein a ratio of an amount by weight ofblock A to an amount by weight of block B is from 10:1 to 1:10.
 2. Acoating composition of claim 1, wherein the polyurethane is synthesizedfrom a mixture comprising a polyol mixture containing predominantlypolycaprolactone diols, an isocyanate mixture having an average NCOfunctionality greater than 1.5 in an NCO:OH ratio of 0.9:1 to 2.5:1 andfunctional components capable of salt formation in aqueous solution. 3.A coating composition of claim 2, wherein the polyurethane issynthesized from a mixture comprising a polyol mixture containing 60 to100% by weight polycaprolactone diols and 0 to 40% by weight of at leastone member selected from the group consisting of polyether polyol,polytetrahydrofuran and polyester polyol containing an average 2 to 4 OHgroups.
 4. A coating composition of claim 2, wherein the polyurethane issynthesized from a polyol mixture containing 80 to 100% by weightpolycaprolactone diols.
 5. A coating composition of claim 2 wherein thepolyurethane is synthesized from a mixture comprising two differentpolycaprolactone diol blocks, wherein the first polycaprolactone diolblock A has an average molecular weight of 500 to 2,500 and a hydroxylvalue of 40 to 225 and the second polycaprolactone diol block B has anaverage molecular weight of 2,500 to 6,000 and a hydroxyl value of 15 to55.
 6. A coating composition of claim 1 wherein the polyurethane issynthesized from an isocyanate mixture containing a composition selectedfrom the group consisting of aliphatic and aromatic isocyanates, havingan average NCO functionality above 1.5.
 7. A coating composition ofclaim 1 wherein the polyurethane is synthesized from at least oneisocyanate selected from the group consisting of branched diisocyanatesand cycloaliphatic diisocyanates.
 8. A coating composition of claim 1wherein the polyurethane contains the residue of at least oneco-condensed component capable of salt formation in aqueous solutionselected from the group consisting of dihydroxycarboxylic acids anddihydroxysulfonic acids.
 9. A coating composition of claim 1 wherein thepolyurethane contains the residues of isocyanate-reactive diamines aschain-extending agents.
 10. A coating composition of claim 1 wherein thepolyurethane dispersion has a solid content of 30 to 60% by weight. 11.A coating composition of claim 1 containing the polyurethane dispersionin a quantity of 5 to 80% by weight.
 12. A coating composition of claim1 which contains water in an amount of 2 to 80% by weight, awater-miscible organic solvent in an amount of 0 to 50% by weight andtypical additive in an amount of 0 to 80% by weight.
 13. A coatingcomposition of claim 9 wherein the polyurethane contains nochain-extending agent.
 14. A coating composition of claim 4 wherein thepolyol mixture consists essentially of 100% polycaprolactone diols. 15.A coating composition of claim 6 wherein the average NCO functionalityis from 2 to
 3. 16. A coating composition of claim 10 wherein thepolyurethane dispersion has a solids content of from 35% to 55% byweight.
 17. A coating composition of claim 11 containing from 20 to 75%by weight of the polyurethane dispersion.
 18. A coating composition ofclaim 17 containing from 50% to 70% by weight of the polyurethanedispersion.